GOC – Week 5

The code is so close to be working now; installing ATLAS it led us to a missing API package within the code. This package is responsible for finding the catalogues that the code needs to work when SWARP takes the scamp calibrations, this is believed to be because the CCD readings from the centre of the four CCDs as opposed to the top centre of the individual CCDs.  

The rest of the week has been spent analysing previously reduced images from Hubble. Emma has implemented the code that is used to plot the isochrones and has been testing the effects that different values of: distance, metallicity and age will have. This code is imported from Dartmouth library using the ‘isochrone’ package that Python has. This code required an initial value for: distance, age and metalicty in order for a plot to be produced, from this we could adjust the values until the isochrone could produce a perfect fit onto our data.  Using our results from the literature search for initial values of approximately 10e9 years, 10e3PC we implemented the code a produced a plot as shown below.

The isochrone was quite far off from our data so we continued to search for values testing different apertures and managed to get a close fit.

However, we came across a problem. Changing the value of metallicity should shift our isochrone horizontally but it seems to have no effect. Emma believes this could be due to the way that the code calls out the variable and hopes that this be resolved next week. To see how close our results were we took only the inner region of M3 so we could accurately see how well the turnoff point aligns. By performing this we managed to see that they nearly match. A shift in metallicity will produce a near perfect fit at an age of 11.4e9 years.

From performing this we can learn how the main sequence of clusters change with age, the turnoff point will correspond to the point the stars evolve off the main sequence line hence show the age.

Hamish has been working on plotting HR diagrams. In order to do this Anaconda needed to be downloaded Python. First we needed to run SExtractor on M71 in the violet filter, this filter was picked since it is further away from the IR for a greater shift for metallicity. Using Topcat we took the catalogues that were created by SExtractor and found one that matched up well with it. Hamish managed to find one that had 210 matches. From here we can take the difference from magnitude of zero point and magnitude in the catalogue. Plotting a histogram and writing a Python code to find the median gave us a Zero point of 28.89. Running the code with the new zero point and errors created a table of data with errors which can be used to produce HR diagrams

There is a notable about of noise present within the HR diagrams which we believe to be the results of background stars that are not part of our cluster but are still picked up be SExtractor. Hamish hopes to be able to filter out the noise.

Our result of the week is the isochrone plot of the outer region of M3 with 1arcsecond apertures at a distance of 9600PC with an age of 11.4e9yrs since it demonstrates how well the isochrone can fit over reduced data which can allow different properties of a cluster to be determined despite the metallicity not aligning properly due to a small issue with the code.

Thomas Harrison

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